Flutter: A build function returned null - flutter

Question

I have a StatefulWidget for displaying page with data, and I am using setState for returning the page, but when I am running apps show error like this:
[1] : https://imgur.com/a/7bJJSLI "screenshot"
this is my code
import 'package:flutter/material.dart';
import 'package:codelab_dicoding/data.dart';
import 'package:codelab_dicoding/detail.dart';
class BreakFast extends StatefulWidget{
#override
_BreakFastState createState() => _BreakFastState();
}
class _BreakFastState extends State<BreakFast>{
List<Container> daftarBreakfast = List();
#override
Widget build(BuildContext context) {
// TODO: implement build
Future <_BreakFastState>_breakfast() async {
for (var i = 0; i < breakfast.length; i++) {
final namaMakanan = breakfast[i];
final String gambar = namaMakanan["gambar"];
final String bahan = namaMakanan["bahan"];
daftarBreakfast.add(Container(
padding: EdgeInsets.all(10.0),
child: Card(
child: Column(
children: <Widget>[
Expanded(
// tag: namaMakanan['nama'],
child: Material(
child: InkWell(
onTap: () =>
Navigator.of(context).push(new MaterialPageRoute(
builder: (BuildContext context) => Detail(
nama: namaMakanan['nama'],
gambar: gambar,
bahan: bahan
),
)),
child: Image.network(
gambar,
fit: BoxFit.cover,
),
),
),
),
Padding(
padding: EdgeInsets.all(10.0),
),
Text(
namaMakanan['nama'],
style: new TextStyle(fontSize: 20.0),
)
],
))));
}
}
setState(() {
return BreakFast();
});
}
}
Is there something wrong with my code? I just omitted some variables for simplicity.

Answer 1

There are couple of mistakes you were making, like you were using setState inside build() and you also had your _breakfast() inside the build(). Check out this code, it is working.
class BreakFast extends StatefulWidget {
#override
_BreakFastState createState() => _BreakFastState();
}
class _BreakFastState extends State<BreakFast> {
List<Container> daftarBreakfast = List();
// put it outside build()
Future<_BreakFastState> _breakfast() async {
for (var i = 0; i < breakfast.length; i++) {
final namaMakanan = breakfast[i];
final String gambar = namaMakanan["gambar"];
final String bahan = namaMakanan["bahan"];
daftarBreakfast.add(Container(
padding: EdgeInsets.all(10.0),
child: Card(
child: Column(
children: <Widget>[
Expanded(
// tag: namaMakanan['nama'],
child: Material(
child: InkWell(
onTap: () => Navigator.of(context).push(new MaterialPageRoute(
builder: (BuildContext context) => Detail(nama: namaMakanan['nama'], gambar: gambar, bahan: bahan),
)),
child: Image.network(
gambar,
fit: BoxFit.cover,
),
),
),
),
Padding(
padding: EdgeInsets.all(10.0),
),
Text(
namaMakanan['nama'],
style: new TextStyle(fontSize: 20.0),
)
],
))));
}
}
#override
Widget build(BuildContext context) {
// return BreakFast();
return FlutterLogo(size: 400); // try this
}
}